Dewatering pelletizer apparatus

ABSTRACT

Disclosed is a dewatering pelletizer apparatus and method for dewatering and reducing the size of wet polymeric material. The apparatus is comprised of an elongated barrel housing having an input end and an output end. Escape passages are provided in the barrel wall to permit the escape of liquid from the interior of the housing. A rotatable shaft having screw flights therein is disposed axially within the housing with one end of the shaft disposed within the output end of the housing. A bearing boss is supported within the housing and provides a bearing support for the shaft end. A generally annular screw flight section is secured to the shaft end and is defined by external and internal screw flights. The annular space between the external screw flight and the internal wall of the housing defines a discharge passage for polymeric material. The internal screw flight of the annular screw flight section is disposed closely adjacent the bearing boss thereby preventing polymeric material from entering the bearing chamber. An oil seal is provided adjacent the bearing and extends from the bearing boss into contact with the shaft. A secondary internal screw flight member is secured to the shaft closely adjacent an annular sealing wall extending from the bearing boss. The secondary internal screw flight member and the internal screw flight of the annular screw flight section cooperate to prevent polymeric material from entering the bearing chamber. A generally circular die plate is secured to said housing in blocking relationship to the output end thereof. A plurality of circumferentially spaced apertures are defined in the die plate. A high-speed cutting blade is disposed adjacent the die plate and is adapted to cut the extruded polymeric material into flakes as it emerges from the die plate.

United States Patent [72] Inventors BillyJ.Redding;

John T. Steadman; Lorel J. Br gg, St. Albans, W. Va. [21] AppLNo.765,758 [22] Filed Oct. 8, 1968 [45] Patented May 18,197] [73] AssigneeGoodrich GulfChemicals, Inc.

[54] DEWATERING PELLETIZER APPARATUS 10 Claims, 6 Drawing Figs.

[52] U.S.Cl. 18/12 [51] lnt.CI 132913100 [50] FieldofSearch 18/12(A), 12(SF), 12 (S1), 12 (SR), 12 (S2) [56] References Cited UNITED STATESPATENTS 2,401,236 5/1946 Fielitz 18/12 2,524,751 11/1950 Beager 18/122,948,922 8/1960 Meslsatetal.. 18/12 3,023,455 3/l962'Geigeretal. 18/123,285,163 11/1966 Burner 18/18 3,331,101 7/1967 Thomas 18/12 3,363,5871/1968 l-larringtonetal. 18/12 3,364,523 1/1968 Shippers 18/12 PrimaryExaminer-Frank T. Yost Attorneys-J. Hughes Powell and Robert W. WilsonABSTRACT: Disclosed is a dewatering pelletizer apparatus and method fordewatering and reducing the size of wet polymeric material.

The apparatus is comprised of an elongated barrel housing having aninput end and an output end. Escape passages are provided in the barrelwall to permit the escape of liquid from the interior of the housing. Arotatable shaft having screw flights therein is disposed axially withinthe housing with one end of the shaft disposed within the output end ofthe housing. A bearing boss is supported within the housing and providesa bearing support for the shaft end. A generally annular screw flightsection is secured to the shaft end and is defined by external andinternal screw flights. The annular space between the external screwflight and the internal wall of the housing defines a discharge passagefor polymeric material. The internal screw flight of the annular screwflight section is disposed closely adjacent the bearing boss therebypreventing polymeric material from entering the bearing chamber. An oilseal is provided adjacent the bearing and extends from the bearing bossinto contact with the shaft. A secondary internal screw flight member issecured to the shaft closely adjacent an annular sealing wall extendingfrom the bearing boss. The secondary internal screw flight member andthe internal screw flight of the annular screw flight section cooperateto prevent polymeric material from entering the bearing chamber. Agenerally circular die plate is secured to said housing in blockingrelationship to the output end thereof. A plurality of circumferentiallyspaced apertures are defined in the die plate. A high-speed cuttingblade is disposed adjacent the die plate and is adapted to cut theextruded polymeric material into flakes as it emerges from the dieplate.

PATENTED m 1 a 1911 SHEET 1 OF 5 G T A wwu H b -B V N L.( R

W W O B ww memtnuavwm V 3,578,740

SHEET 3 OF 5 INVENTORS BILLY J. REDDING JOHN T. STEADMAN LOREL J. BRAGGATTORNEY.

SHEET 0F 5 INVENTORS BILLY J. REDDING JOHN T. STEADMAN LOREL J. BRAGG BYAT TOR NEY.

mama) mm a m PAIEII EIIIIIIBIIII 3578.740

- SHEETSUFS WATER POLYMERIC MATERIAL SHAKER SHAKER SCREEN FIRST wATERWASH wl TE sEcoND WATER FILM WASH To WRAPPER BALER WASTE E DRYER GRINDERP R E S I sPIRAL CONVEYOR uNIT coNTAINER FIG. 5 (PRIOR ART) POLYMERICWATER HAKER s MATERIAL SCREEN WATER SHAKER SCREEN FIRsT WASH w ER wAsTEEXgfi W ER v WASTE DEWATERING FILM I PELLETIZER wRAPPER BALER I nun.DRYER To 1y I wAsTE UNIT coNTAINER 6 I INVENTORS BILLYJ. REDDING JOHN ISTEADMAN LOREL J. BRAGG ATTORNEY DEWATERING PELLETIZER APPARATUSBACKGROUND OF THE INVENTION This invention relates to a dewateringpelletizer apparatus and method for the dewatering and size reduction ofwet polymeric material.

SBR synthetic rubber is a copolymer of butadiene and styrene. Generallythere are four steps utilized in the production of SBR rubber: pigmentand monomer preparation, polymerization in the reactors, removal andrecovery of unreacted butadiene and styrene from the latex, and thecoagulation and recovery of the polymer from the stripped latex.

After preparation of the pigments and monomers, polymerization isconducted in an emulsion of the raw materials in water. Upon completionof the polymerization reaction, the unreacted butadiene and styrene arestripped from the emulsion of rubber in water. Subsequently, an acid oran acid salt is added to the emulsion to coagulate the rubber containedtherein into a form which, in the industry, is termed crumb.

The more specialized rubbers, which have been developed in recent years,are produced by polymerization in the presence of an organic solvent toform a cement. Upon completion of the polymerization, the organicsolvent is stripped from the crumb as the cement is coagulated. Althoughcoagulation can be conducted in several different ways, most of themethods result in the employment of water as the carrier for the rubbercrumb.

As a consequence of the methods by which various raw materials arepolymerized to elastomeric products, and because of the means ofremoving the unreacted components and/or solvents from these materials,most such elastomers finally occur as a water slurry. Since the end useof such elastomers requires the elimination of water and volatilesolvents in general, this water must be substantially completely removedfrom the elastomeric material.

A common method of removing water from wet polymeric material is tofirst pass the material through a dewatering press having interruptedscrew flight sections. The screw flights literally squeeze moisture fromthe material. The product is thereafter discharged from the pressthrough some type of sizing device to reduce particle size and thusfacilitate the thermal removal of the remaining moisture.

Upon removal from the dewatering press the polymeric material then dropsinto a hammermill-type disintegrator or grinder where the chunks ofmaterial are shredded.

The shredded product is thereafter passed through a perforatedapron-type hot air dryer where substantially complete drying to about0.50 percent water is accomplished in approximately 2 hours.

A typical dewatering press of the prior art includes an elongatedcylindrical barrel housing or enclosure built up from an assembly ofbarrel bars held together by ring retainers. The barrel bars areslightly spaced to provide escape passages through which liquid can beforced from the housing. Axially disposed within the barrel is arotatable shaft including several interrupted screw flight sectionsmounted thereon. Inorder to prevent the shaft from contacting theinternal barrel wall (resulting in excessive wear of the screw flightsand the barrel liner) bearing supports are usually provided at eitherend of theshaft. Because of the difficulty of mounting a bearing withinthe barrel it is customary to extend the shaft completely through thebarrel while supporting the ends of the shaft by means of bearingsmounted outside of the barrel. The primary difficulty encountered inmounting a shaft bearing within the barrel is that the polymericmaterial and vapors under pressure will normally destroy the bearingafter a short amount of use. Further, with a bearing mounted within thebarrel, great difficulty is normally encountered in providing sufficientlubrication for the bearing.

Consequently, it is customary in the prior art to support the rotatingshaft of the dewatering press by means of external bearings supportedoutside of the barrel. Since the die plate of the dewatering press isnormally mounted at the output end of the barrel, it is thus necessaryfor the rotating shaft to pass through the die plate in order to besupported by the external hearing. The die plate thus must be fabricatedwith a large hole through the center thereof which serves both to weakenthe die and, with the shaft extending through the die, defines anannular ring between the shaft and the die through which large pieces ofpolymeric material may extrude to cause contamination problems.

A further characteristic of prior art dewatering presses is the cutterstructure wherein the cutter blades are secured to the shaft and aredriven at the same speed as the shaft. The cutter blades thus rotate atthe same relatively slow rate of speed as the screw flight sectionsproducing rough polymeric particles of rather large size necessitatingthe use of a grinder before oven drying.

This invention provides a dewatering pelletizer in which the end of therotating shaft is completely supported within the barrel, and the dieplate is free of any apertures other than those provided for the purposeof extrusion of the polymeric material.

This invention further provides a cutter structure wherein the cutterblades are driven independently of the shaft at a relatively high rateof speed to produce wafer thin polymeric particles suitable forimmediate drying in an oven dryer.

A further characteristic of the prior art dewatering press is that thescrew flights, increasing in size as they progress toward the dischargeend of the barrel, are usually the cutflight or interrupted type. SinceSBR rubber tends to pack under pressure, it must not be confined in anarrow annular space and thus the screw flights must be interrupted.Furthermore, SBR rubber must be masticated by the breaks in the screwflights in order to prevent agglomeration which would entrap moisture inthe material and render the application of heat for drying off moistureineffective.

It has been found that polyisoprene rubber cannot be dewateredsatisfactorily by the conventional SBR dewatering press. Differences inthe mechanical properties of SBR and polyisoprene rubber provide thebasic reason for the failure of the SBR type dewatering press tosuccessfully dewater polyisoprene rubber. Unlike SBR, polyisoprene is astough and elastic as natural rubber. It is the toughness and elasticityof polyisoprene that renders the drying thereof difficult as will bedescribed hereafter.

In processing SBR rubber it is normal for the product to pass throughthe outlet of the dewatering press to be chopped into piecesapproximately 1 cubic inch in volume by a cutter rotating with the screwshaft at the relatively slow speed of approximately 75 r.p.m. Theproduct then drops into a hammermill-type disintegrator or grinder wherethe chunks are shredded and thereafter blown to a thermal dryer. Theporosity of the SBR material is such that heat will remove the remainingwater from the product.

For polyisoprene rubber, however, the SBR dewatering press is inadequatefor drying purposes because (a) the fluidic tendencies of polyisoprenematerial cause it to stretch and wrap around the slow speed cutter andeventually fall off in large chunks of several cubic inches volume, (b)polyisoprene will not shred in a disintegrator, and (c) polyisoprene isessentially nonporous and hence cannot be dried thermally unless it isfirst reduced to extremely small particle size.

Therefore, in order to completely dry the polyisoprene rubber productthat has been dewatered, it must be cut to a particle size or thicknesssmall enough that water molecules can escape from the surface of thematerial and not depend on the porosity of the material for removalthereof. Thus, the conventional system of dewatering and drying SBRrubber is ineffective with respect to polyisoprene rubber.

This invention provides an apparatus and method for the dewatering andsize reduction of polyisoprene rubber and wherein the product can beblown directly from the dewatering pelletizer to a thermal dryer thuseliminating the necessity BRIEF SUMMARY OF THE INVENTION Brieflysummarized, this invention provides a dewatering pelletizer apparatusand method for the dewatering and size reduction of wet polymericmaterial.

The apparatus of this invention comprises in combination an elongatedbarrel housing having an axis, an input end and an output end. Means areprovided in the wall of the barrel housing to permit the escape ofliquid therefrom. A rotatable shaft having at least a portion thereofdisposed axially within the housing is supported for rotation thereinwith an end of the shaft disposed within the output end of the housing.Screw flight sections are carried by the shaft in order to advance andcompact the material within the housing. A die plate is secured to thehousing at the output end thereof and includes a plurality ofcircumferentially spaced apertures for the passage of polymeric materialtherethrough. The die plate also includes a bearing boss for the purposeof supporting the shaft end within the output end of the housing. Agenerally annular screw flight section is secured to the shaft at theend thereof and is defined by external and internal screw flights. Theannular space between the external screw flight and the internal wall ofthe housing defines a discharge passage for polymeric material at thehigh-pressure side of the die plate. The internal screw flight of theannular screw flight section is disposed closely adjacent the bearingboss extending from the die plate whereby polymeric material isprevented from entering the bearing chamber partially defined by thebearing boss. A secondary internal screw flight member cooperates withan annular sealing wall extending from the bearing boss in order tofurther inhibit the flow of polymeric material into the bearing chamber.A seal is provided immediately adjacent the bearing in order to retainlubricating oil in the bearing chamber. A high-speed cutter is disposedadjacent the external surface of the die plate and is adapted to reducethe size of the polymeric material as it passes through the die plate.

The method of this invention for dewatering and reducing the size of wetpolymeric material comprises the steps of:

l. I. Dewatering wet polymeric material;

2. Extruding said material through a die plate;

3. Shearing the extruded material into thin particle form as it emanatesfrom the die plate; 4. Drying the particles; 5. Recovering the driedparticles.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete description of theapparatus and method of this invention will now be made with referenceto the attached drawings in which:

FIG. 1 is a side elevational view, partially cut away and partially insection, of the dewatering press of the prior art;

FIG. 2 is a side elevational view, partially cut away and partially insection, of the dewatering pelletizer of this invention;

FIG. 3 is an enlarged sectional view of the die plate area of theapparatus of this invention and showing in detail the annular screwflight section, the secondary internal screw flight member, and the oilseal of the bearing chamber;

FIG. 4 is an enlarged sectional view similar to FIG. 3 and showing amodification of the oil seal of FIG. 3;

FIG. 5 is a flow chart of the process steps employed by the prior art insubstantially completely drying rubber; and

FIG. 6 is a flow chart of the method of this invention for substantiallycompletely drying rubber.

DESCRIPTION OF THE PRIOR ART Before describing the dewatering pelletizerapparatus and method of this invention, attention will first be directedto FIG. 1 wherein there is shown a dewatering press of the prior art.Dewatering press 10 of FIG. 1 is defined by a generally cylindricalbarrel housing 12 having an axis 13, an input end 14 and an output end16. The barrel housing 12 is built up from an assembly of barrel bars 17held together by semicircular split ring members clamped in tightengagement by clamping bolts (not shown). The barrel bars 17 areslightly spaced to provide longitudinal escape passages through whichliquid can be forced. The escape passages, however, are not wide enoughto permit the passage of the solid polymeric material.

Disposed axially within the barrel housing 12 is a rotatable shaft 18driven by a gearcase assembly 20 which in turn receives power from asuitable source (not shown). End 22 of shaft 18 is supported forrotation by means of bearings 24 supported by the gearcase assembly 20.The opposite end 26 of shaft 18 is supported for rotation by means of abearing 28 supported by the discharge housing 30.

A plurality of screw flights 34, 36, 38 and 40 are provided on therotatable shaft 18 for the purpose of advancing and compacting polymericmaterial within the barrel housing 12. It will be noted from FIG. 1 thatthe dewatering screw flights 36, 38 and 40 increase in root diameter asthey progress toward the discharge end 16 of the housing. As an exampleof the dimensions of the screw flights, a typical 13 /2 inches SBRdewatering press will have screw flights with diameters increasing from7 to 10 inches.

At the output end 16 of barrel housing 12 there is provided a dischargering 42 and several circumferentially spaced choking bars 44.Circumferentially spaced cutter blades 46 and 48 are mounted on theshaft 18 and cooperate with the fixed circumferentially spaced cutterblades 50 mounted on the discharge housing 30. The respective blades 46,48 and 50 are spaced about the axis 13 of the shaft 18 and may vary innumber although in the prior art embodiment of FIG. 1 sixcircumferentially spaced blade elements are utilized in each set ofblades.

The choking bars 44 may be radially adjusted to not only produce alocalized obstruction to increase the extraction of liquid from thematerial in the press, but also to cause such material to issue from thepress in a predetermined form. As the material issues from the press itis cut by the rotating sets of cutter blades 46, 48 cooperating with thefixed set of blades 50.

By a selective interposition of the choking bars 44 a predeterminedlocalized source of back pressure may be achieved. For a more completedescription of the choking bar structure of the prior art embodiment ofFIG. 1 reference is made to the Ginaven US. Pat. No. 3,288,056 (Cl.-98).

Briefly reviewing the operation of the prior art dewatering press ofFIG. 1, wet polymeric material is introduced into the press at the inputend 14 where it is advanced into the barrel housing 12 by means of thefeed screw flight 34. The feed screw flight 34 forces the material intothe dewatering screw section of the barrel housing 12 where theprogressively larger root diameter screw flights 36, 38 and 40 squeezemoisture from the product and discharge it through the longitudinalslits defining escape passages in the wall of the barrel housing 12. Thecompacted material is thereafter passed through the discharge ring 42and the choking bars 44 after which it is reduced to size by means ofthe rotating cutter blades 46 and 48.

THE PROBLEM DEFINED The dewatering press of the prior art as shown inFIG. 1 was designed primarily for the dewatering of regular SBRpolymers. However, it has been found that this type of press will notperform satisfactorily on polyisoprene polymers such ascis-l-4-polyisoprene due to the differences in the elasticity andtoughness of the respective polymers.

In processing SBR polymers it is normal for the material to pass throughthe discharge end of the press and to be chopped into piecesapproximately I cubic inch in volume by the blades 46, 48 (FIG. 1)rotating with the shaft 18 at a relatively slow speed of about 75 r.p m.The product then drops into a hammermill-type disintegrator or grinderwhere the chunks are shredded and thereafter conveyed to a thermaldryer. The porosity or conventional SBR material is such that the heatof the thermal dryer will substantially completely remove the remainingmoisture from the product.

For polyisoprene type polymeric material, however, the conventional SBRapparatus is not satisfactory due to a number of factors. The elasticityand toughness of polyisoprene polymeric material cause it to stretch andwrap around the relatively slow rotating cutter blades 44, 46 of theprior art press of FIG. 1. Having become entwined in the cutter blades,the polyisoprene material eventually drops off in large chunks ofseveral cubic inches volume. When conveyed to the hammermiIl-typedisintegrator, the polyisoprene material will not shred due to itstoughness and thus approximately the same size pieces emerge from thedisintegrator as are initially fed into it. Since the polyisoprenepolymeric material is essentially nonporous, it cannot be driedthermally unless it is first reduced to extremely small particle size.

Thus, in order to effectively dry polyisoprene polymeric material, itmust first be shredded to a particle size or thickness small enough forthe water molecules to escape from the surface of the material since theproduct is nonporous. Therefore, since the dewatering press of the priorart is not capable of reducing polyisoprene material to a relativelysmall particle size, drying of polyisoprene material through the use ofthe prior art press with thermal dryers has been ineffective.

THE CONTRIBUTION Attention is now directed to FIG. 2 wherein adewatering pelletizer embodying the principles of this invention isshown. The dewatering pelletizer 52 of FIG. 2 includes a barrel housing54 defined by a plurality of dewatering screen bars 56. As in the priorart dewatering press of FIG. 1, the dewatering screen bars 56 of FIG. 2are slightly spaced to provide escape passages through which liquid canbe forced. These passages, however, are not wide enough to permit escapeof solid material. A rotatable shaft 58 is disposed axially withinhousing 54. End 60 of shaft 58 is disposed axially within housing 54.End 60 of shaft 58 extends through the barrel housing 54 and issupported for rotation by means of a bearing 62 which may be mountedwithin the frame of a suitable gearbox 63. It is to be understood thatthe shaft end 60 of FIG. 2 is adapted to be driven by means of anysuitable power source through gearbox 63 much in the same manner as thedewatering press of FIG. 1. In the interest of brevity, the completedetails of the gearbox 63 will not be described as they do not compriseany part of the invention.

Barrel housing 54 is provided with an input end 64 in the foim of a feedbox into which wet polymeric material is disposed.

Shaft 58 is provided with several screw flight sections in-- cluding inthis embodiment a feed screw flight 66 and four dewatering screw flights68, 70, 72 and 74.

It will be noted that whereas the dewatering screw flights 68, 70 and 72are of the cut-flight type with the root diameters thereof slightlyincreasing, the last dewatering screw flight 74 is continuous and in thepreferred embodiment of FIG. 2 increases in diameter at a constant rateover a relatively long screw length. Within the scope of this inventionshould also be considered a constant diameter screw flight 74.

As an example of relative sizes, the diameters of the screw flights 66,68, 70 and 72 in the preferred embodiment are respectively I 1, l l, 12and l2'/2 inches. Screw flight 74 of the preferred embodiment iscontinuous and increases in root diameter at a constant rate over a 24inch length without a break in the flight.

As will be more fully described hereafter the dewatering screw flight 74is defined on the external surface of a generally annular screw flightsection 76 adapted to be secured to the shaft 58.

The inner end 80 of shaft 58 is adapted to be rotatably supported withinthe output end 82 of the barrel housing by means of a shaft bearing 84seated on a bearing seat 86 defined by bearing boss 88 extending fromdie plate 90.

Die plate 90 is adapted to be received within counterbore 92 ofdie-centering ring 94 and is secured thereto by means of suitablefasteners (not shown). Die-centering ring 94 is, in turn, adapted to besecured to the barrel housing 54 at flange 96 by means of bolts 98.

It is thus to be understood that the die-centering ring 94, die plate90, and bearing boss 88 are fixed with respect to the barrel housing 54and serve to support the inner end of housing 12 having an end 26supported outside of the barrel housing 58 within the barrel housing 54.

At this point a comparison may be made between the dewatering pelletizerof FIG. 2 and the prior art dewatering press of FIG. 1. Whereas, theshaft 18 of FIG. 1 extends completely through the barrel housing bymeans of bearing 28 and discharge housing 30, the shaft 58 of FIG. 2terminates inside the barrel housing at the high-pressure side of thedie plate and, in the preferred embodiment of FIG. 2, is rotatablysupported by bearing boss 88 of die plate 90. The advantages of thestructure of FIG. 2 will become apparent as the description proceeds.

The die plate 90 of FIG. 2 is provided with a plurality ofcircumferentially spaced apertures 100, 102, 104 and 107 (FIG. 3, 4). Asshown in FIG. 2 the apertures are clustered at various radii from theaxis 105 of the die plate and are generally disposed within the path ofpolymeric material as it is discharged from annular space 106 defined byscrew flight 74 and the internal wall of barrel housing 54.

It is to be noted that except for the rows of apertures 100, 102 and104, the die plate 90 is otherwise impervious to the flow of materialtherethrough. The necessity for providing a central passage for therotating shaft (as when the shaft is supported externally of the housingas in FIG. 1) -has been eliminated.

As the polymeric material is extruded through the rows of apertures 100,102 and 104 of FIG. 2, it is cut to size by means of spaced cutterknives 108 carried by shaft 110. In the preferred embodiment of thisinvention shaft 110 is provided with a total of eight equally spacedcutter knives 108 each having a sharp leading edge. One end of shaft 110is supported for rotation by means of bearing 112 disposed within asuitable recess in the die plate 90. Shaft 110 is further supported forrotation by means of bearing 114 carried by cutter housing 116. Cutterhousing 116 is, in turn, secured to die-centering ring 94 by means offasteners 118. As shown in FIG. 2, cutter housing 116 defines a portionof an air conveyor system that is utilized to blow the polymeric productto a thermal dryer. Suitable rotation means (not shown) may be employedsuch as an electric motor to drive shaft 110 at 115 thus independentlyrotating the cutter knives 108 to cut the polymeric product as it isextruded from the die plate 90.

In comparison the the prior art dewatering press of FIG. 1 it should benoted that shaft 110 of FIG. 2 is driven indepen dently of the shaft 58to provide a cutter speed independent of the dewatering screw flightspeed. Thus, whereas in the prior art dewatering press of FIG. 1 thecutter blades 46, 48 rotate at the same relatively slow speed as thedewatering screw flights 36, 38 and 40 (around 75 rpm), the cutterknives 108 of FIG. 2 are driven at a relatively high rate of speed(approximately 1,750 rpm.) thus to cut the extruded material into flakesabout 1/64 inch thick and inch in diameter or smaller, depending uponthe rate of production.

Since the product is cut to relatively small particle size bythehigh-speed cutter knives 108, it is blown directly from the cutterhousing 116 to a thermal dryer by means of an air conveyor system forthe substantially complete removal of any remaining moisture without thenecessity of passing through a hammermill-type disintegrator or grinderas is characteristic of prior art processes utilizing the dewateringpress of FIG. 1. It is to be understood that the housing 116 of FIG. 2may have suitable conduit attached to it such that forced air may beutilized to blow the extruded and cut material flakes directly to athermal dryer.

REVIEW OF OPERATION To briefly review the operation of the dewateringpelletizer of FIG. 2 the wet polymeric material is introduced into thebarrel housing 54 at the input end 64. The material is thereafteradvanced by feed screw flight 66 into the dewatering section of thehousing where moisture is squeezed from the material by means of thedewatering screw flights 68, 70, 72 and 74. The final dewatering screwflight 74 is a relatively long continuous screw of increasing diameterdefining, with the internal wall of the housing 54, a narrowsubstantially annular space 106. The material is thereafter extrudedthrough the several rows of apertures 100, 102 and 104 where it is cutinto particle form by means of the high-speed cutter knives 108.

It has been found that the relatively long, continuous, increasingdiameter screw flight 74 defining the generally annular space 106provides dewatering to a much greater degree than that of theconventional structure of FIG. 1. A product having 2-3 percent moistureis common with the dewatering pelletizer of FIG. 2 as compared to aproduct containing 8- l4 percent moisture when passed through thedewatering press of FIG. 1.

A principal advantage of supporting the inner end of shaft 58 of FIG. 2within the barrel housing 54 is that the cutter knives may be mountedindependently of the screw flights. The cutter knives may thus be turnedat a higher rate of speed than the screw flights to produce smallproduct particles.

Further, the termination of the shaft within the barrel hous ingeliminates the necessity to provide a large hole in the center of thedie plate. This hole not only weakens the die plate but it also definesan annular space between the shaft and the die plate through whichrather large product particles could extrude producing contaminationproblems.

BEARING SEALING Since the shaft 58 of FIG. 2 terminates at the outputend of the barrel housing at the high-pressure side of the die plate 90,this invention provides a seal to keep the polymeric product out of thebearing thus to preserve the life of the bearing.

Conventional sealing structures generally cannot withstand the highpressures of the barrel interior and thus cannot provide sustainedsealing of the chamber surrounding the bearing. In the dewateringpelletizer of this invention as shown in FIGS. 2 and 4, the generallyannular screw flight section 76 is provided with both an externaldewatering screw flight 74 and a primary sealing internal screw flight122. The primary sealing screw 122 is generally similar to thedewatering screw flight 74 and is adapted to be disposed closelyadjacent the cylindrical surface 124 of bearing boss 88 and acts toforce material toward the die plate 90 from the space 126. A generallyannular sealing wall 128 extends from the bearing boss 88. The externalsurface of sealing wall 128 defines a cylindrical extension of surface124 and cooperates with the primary internal screw 122 to force allpolymeric material that may be compacted into the space 126 toward thedie plate 90.

A secondary sealing internal screw flight member 129 having a screwflight surface 130 is disposed closely adjacent the internal surface ofsealing wall 128. Secondary sealing internal screw flight member 129 issecured to a radial shoulder of screw flight section 76 by means offasteners 132. The thread direction of the secondary internal screwflight 130 is opposite to that of the primary internal screw flight 122such that material within the space 134 will be forced toward the outerextremity 136 of the sealing wall 128 and thereafter will be conveyed tothe die plate 90 by means of the primary internal screw flight 122.

It will be noted from FIG. 4 that the various sealing elements includingthe screw flight section 76, sealing wall 128, and secondary internalscrew flight member 129 are coaxial. Rotation of shaft 58 producesrotation of the secondary internal screw flight member 129 and theprimary internal screw 122 about the sealing wall 128. Any polymericproduct within the screw flight section 76 is thus forced toward the dieplate 90 by means of the rotating internal screw flights 122, 130(having an opposed thread sense).

Depending upon the type of bearing utilized to support the inner end ofthe shaft 58 carrying the screw flight sections, this invention providesfor a seal extending from the bearing boss 88 and contacting shaft 58such that lubricating oil may be retained in bearing chamber and thepurity of the oil maintained. This seal also prevents the entry of steamand other vapors into the bearing chamber which could shorten the lifeof the bearing.

In FIG. 3, one form of the oil and vapor seal is shown including amechanical seal 138 providing sealing between the rotatable shaft 58 andextension 140 of bearing boss 88. The

integrity of bearing chamber 120 is thus preserved.

An alternate embodiment of the lubricating oil and vapor seal is shownin FIG. 4 wherein a seal holder 142 is attached to bearing boss 88 bymeans of fastener 144. A seal 146 fabricated from elastomeric or othersuitable material is carried by seal holder 142 and contacts theexternal surface of shaft 58 thus to provide sealing of bearing chamber120.

Lubricating oil may be supplied to bearing chamber 120 as by means of asuitable internal feed passageway (not shown) defined in the die plateassembly.

Briefly reviewing the oil and vapor sealing structure of the apparatusof this invention, the seals 138, 146 of FIGS. 3 and 4 are designedprimarily to contain lubricating oil within the bearing chamber 120 thusto provide a continuous source of lubrication for the bearing 84. Seals138, 146 further isolate bearing 84 from harmful steam and other vaporssqueezed from the polymeric material by the dewatering screw flights.

Screw flights 122, cooperating with sealing wall 128 inhibit the flow ofpolymeric material into bearing area.

METHOD This invention is also directed to a method for dewatering andreducing the size of polymeric material and in'particular ofcisl-4-polyisoprene.

The prior art method for drying SBR type polymeric material is shown inFIG. 5. After polymerization the wet polymeric material is passedthrough a first and second water wash. After the second water wash therubber-water slurry is passed across a shaker screen where the moisturecontent of the rubber is reduced to about 50 percent. From the shakerscreen the product drops into the input end of a dewatering press wherea feed screw forces the material into the dewatering screw section ofthe press. In the dewatering section progressively increasing rootdiameter screw flights squeeze moisture from the product. This moistureis passed to waste through longitudinal slits in the barrel housing ofthe press as previously described. The material is thereafter passedthrough the discharge end of the press where it is reduced to arelatively large particle size by means of rotating cutter blades.

In the prior art process for the dewatering and size reduction of SBRrubber, as shown in FIG. 5, the relatively large particles from thedewatering press are conveyed into a hammermill-type disintegrator orgrinder where they are shredded. The material is thereafter conveyed toa dryer where substantially all of the remaining moisture is removed. Atthe discharge of the dryer a spiral conveyor lifts the product to abaler where final packaging takes place.

This invention provides for a method for dewatering and reducing thesize of wet polymeric material and wherein the dewatering pelletizeraccomplishes both the dewatering and complete size reduction of thematerial making it possible to eliminate the separate grinding step ofthe prior art method.

Thus as is shown in FIG. 6 the polymeric material is passed through afirst and second wash where it is then passed across a shaker screen toremove a substantial amount of moisture. From the shaker screen theproduct is led into a dewatering pelletizer where the material is bothdewatered and reduced in size to flake form. After discharging from thedewatering pelletizer, the product flakes are blown to a thermal dryerby means of an air conveyor system. It is to be understood that thedewatering pelletizer as shown schematically in FIG. 6 is of the typeshown in FIG. 2. After drying the product flakes are blown to a baler bymeans of an air conveyor where final packaging takes place. Since theproduct coming from the dryer is in the form of flakes it is sometimesdesirable to employ means to compact the material prior to baling inorder to prevent undue loss thereof in the packaging operation.

The method steps of this invention will be described now with referenceto FIG. 6. The method comprises the steps of: l. Dewatering wetpolymeric material. As used herein the word dewatering denotes theremoval of liquid from wet polymeric material; the amount of liquidremoved being less than that required to achieve complete dryness. Inthe preferred embodiment of this invention the dewatering method step iscarried out as by providing a barrel housing 54 (FIG. 2) having an inputend 64 and an output end 82 and including escape passageways between thedewatering screen bars 56 defining the housing wall. A rotatable shaft58 is provided within the housing wall. Shaft 58 includes screw flightmeans 66, 68, 70, 72 and 74 thereon. Shaft 58 is supported at one end 80by means of a bearing 84 disposed within the output end of the housing.The opposite end of shaft 58 is supported by means of bearings 62carried by the gear case assembly 63. Dewatering is accomplished as byrotating shaft 58 thereby advancing the wet polymeric material intohousing 54 where the material is compacted and masticated by therotating screw flight means of increasing diameter thus to squeezeliquid from the material.

2. Extruding said material through a die plate. In the preferredembodiment of this invention the extruding method step is carried out asby forcing the material through apertures 100, 102, 104 and 108 of dieplate 90 by means of the rotating screw flight 74. Immediately adjacentthe high-pressure side of the die plate 90 the polymeric material iscompacted into a relatively narrow generally annular space 106. Thematerial inventory immediately behind die plate 90 is thus considerablyreduced when compared to the inventory of material within any otherportion of barrel housing 54. The apparatus of the preferred embodimentwhich carried out the extruding method step of this invention alsoprovides sealing means to prevent polymeric material and vapors fromcoming into contact with the bearing supporting the inner end of therotating shaft. As previously described with respect to FIG. 3, thissealing structure is defined by the screw flights 122, 130 cooperatingwith sealing wall 128 which flights function to prevent the entry ofpolymeric material into the bearing chamber 120. Mechanical seal 138functions to prevent the entry of vapor into bearing chamber 120 whileserving to retain. lubricant in the chamber.

3. Shearing the extruded material into thin particle form as it emanatesfrom the die plate. IN the preferred embodiment of this invention theshearing method step is carried out by rotating a set of cutter knivesat a high rate of speed immediately adjacent the low-pressure side ofdie plate 90. Cutter knives 108 of FIG. 3 are driven independently ofshaft 58 by means of a separately supported and driven shaft 110. In thepreferred embodiment of this invention blades 108 rotate at a rate ofspeed of approximately 1,750 r.p.m. as compared to a rate of speed of 75r.p.m. of the shaft 58. In the preferred embodiment of this inventionthe cutter blades 108 are provided with a sharp leading edge in order toshear the extruded material as it emanates from the die plate 90. Theshearing method step is accomplished with the aid of inertial forces asit is forced from the die openings. In the preferred embodiment of thisinvention the shearing method step is carried out with an apparatusdefined by tapered apertures in the die plate such as shown in FIG. 3.Tapered apertures contribute to a wafer thin product in the shearingstep by containing and supporting the polymeric material within thebarrel until it is cut by the rotating knife.

4. Drying the particles. As used herein the word drying denotes thesubstantially complete removal of moisture from the material. As shownin FIG. 6 the drying step of this invention is carried out immediatelyafter the shearing step. The necessity of providing an intermediatepelletizer or grinder between the dewatering press and the dryer of theprior art has been eliminated since the wafer thin particle product ofthe dewatering pelletizer of this invention can be immediately driedwithout the necessity of an intermediate grinding step.

5. Recovering the dried particles. The final method step of thisinvention is the recovery of the product from the dryer in a suitableform for further processing into a variety of products. As shown in FIG.6 the recovery step is accomplished by means of a baler. Since theproduct coming from the dryer is in a particle or flake form it may bedifficult to handle in the baler. Thus, it may be desirable to employsome form of compaction means for the particle product before theintroduction thereof into the baler.

While the method of this invention is particularly adapted to processcis-l-4-polyisoprene rubber by dewatering the wet material and cuttingit into thin flakes so that it can be later dried in a thermal dryerwithout the necessity of passing the material into a disintegrator forfurther size reduction; this invention should not be considered aslimited to cis-l-4- polysoprene rubber as it is applicable to polymersin general, particularly other tough, elastic material.

ADVANTAGES OF THE INVENTION The principal advantage of the apparatus andmethod of this invention is that polymeric material such as cis-l-4-polysoprene rubber can be dewatered and cut into small particles so thatit can be substantially completely dried in a thermal dryer. Thenecessity for providing a separate disintegrator or grinder between thedewatering press and the thermal dryer has been eliminated by theapparatus and method of this invention as the product of the dewateringpelletizer is in the form of relatively small particles or flakessuitable for drying in a thermal dryer.

The method and apparatus of this invention reduce the moisture contentof polymeric material from approximately percent to 3 percent whileproducing a product having a particle thickness of approximately l/64 ofan inch. As an example of the operating requirements of the apparatus ofthis invention approximately 200 hp. is necessary to operate thedewatering screws whereas 40 hp. is required for the independentoperation of the cutter mechanism.

Table 1 is a brief summary of some of the physical characteristics ofpolymeric material both before and after dewatering, cutting and dryingin the dewatering pelletizer and thermal dryer. It is to be noted fromFIG. 1 that the moisture content of the material is reduced from about50 percent to about 3 percent in the dewatering pelletizer whereasthermal drying further reduces the moisture content to approximately 0.2percent.

each highspeed cutter knife meets the extruded material while thematerial is supported by the die plate and prior to As will be furtherobserved from table 1, the operating pressure within the dewateringpelletizer varies from atmospheric deformation of the material (due toits tough elastic nature) as 5 pressure to approximately p.s.i. Incontrast to this range of pressure is the range of pressure in theconventional SBR dewatering press from atmospheric to approximately4,000 psi. depending upon the position of the choke mechanism. Theapparatus of this invention provides for relatively low extrusionpressures since the polymeric material is confined in a relatively smallannular space (106, FIG. 2) thereby reducing the material inventory thatis built up behind the die plate. Therefore, the only pressure requiredfor extrusion is that necessary to push the polymer through the dieopenings.

MODIFICATIONS OF THE INVENTION Several modifications of the apparatus ofthis invention are contemplated and should be considered within thespirit of the invention.

In the embodiment of FIG. 2 the bearing boss 88 and sealing wall 128 aredefined as an integral part of the die plate 90. A slight modificationof the die plate structure is shown in FIG. 3 wherein it is to be notedthat the bearing boss 88 is defined by a separate element attached todie plate 90 by means of fasteners 144. Sealing wall 128 of FIG. 3 isfurther defined by a generally annular element secured to the bearingboss 88. Further it will be noted from FIG. 3 that shaft 110 is notdirectly supported by die plate 90 (as is shown in FIG. 2) but rather issupported by a support member 160 secured to the die plate 90 by meansof fasteners 141. The die plate 90 and support member 160 of FIG. 3,however, define a generally impervious member through which polymericmaterial may pass only by means of apertures 100, 102, I04 and 107.

In the embodiment of FIG. 4 the bearing boss 88 is defined by a separateelement attached to die plate 90. As in FIG. 3 the sealing wall 128 ofFIG. 4 is generally defined by an annular element secured to the bearingboss 88.

This invention should not be considered limited to the particularstructure providing rotatable support for the shaft 58 within the barrelhousing. Many additional structures providing support for the rotatableshaft should be considered including those that do not depend from thedie plate 90. Thus, shaft 58 could be supported within the output end ofthe barrel housing by means other than the die plate 90.

In the embodiment of FIG. 4 the walls defining apertures 100, 102, 104and 107 are generally cylindrical. A slightly modified aperture is shownin FIG. 3 wherein the walls defining apertures 100, 102, 104 and 107 areslightly tapered defin ing frustoconical surfaces in the die plate 90.The tapered apertures of FIG. 3 are preferred, in fact, since thecutting knives 108 tend to pull the polymer out of the die plate. Thetapered openings contain the material in the process of extrusionpermitting the sharp leading edge of the cutter knives 108 to producewafer thin particles.

For ease of description the principles of this invention have been setforth in connection with but a single illustrated embodiment thereof. Itis not our intention, however, that the illustrated embodiment nor theterminology employed in describing it be limiting inasmuch as variationsmay be made without departing from the spirit of this invention. Rather,we desire to be restricted only by the scope of the appended claims.

We claim:

I. A dewatering pelletizer for dewatering and reducing the size of wetpolymeric material comprising in combination:

an elongated barrel housing having an axis, an input end and an outputend;

means to permit the escape of liquid from said housing;

a rotatable shaft having at least a portion thereof disposed axiallywithin said housing with an end of said shaft disposed within saidoutput end of said housing;

screw flight means carried by said shaft;

bearing means for rotatably supporting said portion of said shaft insaid housing, said bearing means including a bearing supporting saidshaft end within said output end of said housing and bearing seat meanssupported within said housing;

die plate means secured to said housing and disposed normal to the axisof said housing at said output end thereof, said housing and said dieplate means enclosing said shaft end and said bearing;

sealing means defined by a generally annular screw flight sectionsecured to said shaft to isolate said hearing from polymeric material asit passes through said output end of said housing;

circumferentially spaced apertures in said die plate means for thepassage of polymeric material therethrough;

cutting means adjacent said die plate means and adapted to rotateindependently of said shaft to reduce the size of the polymeric materialas it passes through said die plate means.

2. The invention of claim 1 in which the generally annular screw flightsection secured to said shaft is further defined by external andinternal screw flights;

the space between said external screw flight and the internal wall ofsaid housing defining a generally annular discharge passage forpolymeric material;

said internal screw flight being disposed closely adjacent said bearingseat means whereby polymeric material is prevented from entering thechamber surrounding said bearing.

3. The invention of claim 2 in which said bearing seat means is providedwith a generally annular sealing wall having an inner and outer surfaceand extending from said bearing seat means coaxial with said screwflight section, said outer surface disposed closely adjacent saidinternal screw flight; and

a secondary internal screw flight means is secured to said shaft closeiyadjacent said inner wall.

4. The invention of claim 3 in which said secondary internal screwflight means is further defined by a generally annular element coaxialwith said screw flight section and having a screw flight on the externalsurface thereof.

5. The invention of claim 4 in which said secondary internal screwflight element is operatively secured to said shaft by means offasteners extending through a radial shoulder of said element into aradial shoulder of said screw flight section.

6. The invention of claim 2 in which said bearing seat means is furtherprovided with a seal extending from said bearing seat means into contactwith said shaft whereby lubricating oil can be retained in said bearingand steam and other vapors are precluded from coming into contact withsaid bearing.

7. The invention of claim 1 in which said bearing seat means dependsfrom said die plate means.

8. The invention of claim 7 in which said die plate means is furtherdefined by a generally circular plate secured to said housing inblocking relationship to said output end with said shaft end disposedwithin said housing, the internal wall of said plate including a bearingboss defining said bearing seat means.

9. The invention of claim 8 in which a cutter bearing seat is providedin the external surface of said plate and is adapted to receive arotating cutter driven independently of said shaft.

10. A dewatering pelletizer for dewatering and reducing the size of wetpolymeric material comprising in combination:

an elongated barrel housing defined by a plurality of slightly spacedscreen bars defining escape passages through which liquid can be forced,said barrel housing having an input end and an output end;

a rotatable shaft disposed axially within said housing, said shafthaving a first and extending through said housing and supported forrotation by means of a bearing and adapted to be driven by a suitablepower source, and a second end disposed within said output end of saidbarrel housing;

a plurality of dewatering screw flights carried by said shaft andincluding a generally annular screw flight section adjacent said secondend and defining with the internal wall of said barrel housing agenerally annular space;

a generally annular die plate secured to said housing at said outputend;

a generally circular support member secured to said die plate coaxialwith said rotatable shaft;

a generally annular bearing boss secured to said die plate and disposedcoaxial with said rotatable shaft, said bearing boss including a bearingseat adapted to receive a bearing providing rotatable support for saidsecond end of said rotatable shaft;

vapor sealing means extending from said bearing boss into contact withsaid rotatable shaft, said sealing means and said bearing boss defininga lubrication chamber for said circumfefentia lly spaced taperedapertures in said die plate for the passage of polymeric materialtherethrough;

said generally annular screw flight sectiondefined by external andinternal screw flights;

a generally annular sealing wall having an inner and outer surface andextending from said bearing boss coaxial with said shaft, said outersurface disposed closely adjacent said internal screw flight of saidannular screw flight seca rotatable cutter shaft supported by saidcutter bearing seat and adapted to be driven by an external power sourceindependently of said rotatable shaft;

a plurality of spaced cutter knives mounted on said cutter shaft, eachcutter knife having a sharp leading edge and so positioned with respectto said die plate that they meet the extruded material while thematerial is supported'by the walls of the die plate defining saidtapered apertures as it is forced from said die plate.

2. The invention of claim 1 in which the generally annular screw flightsection secured to said shaft is further defined by external andinternal screw flights; the space between said external screw flight andthe internal wall of said housing defining a generally annular dischargepassage for polymeric material; said internal screw flight beingdisposed closely adjacent said bearing seat means whereby polymericmaterial is prevented from entering the chamber surrounding saidbearing.
 3. The invention of claim 2 in which said bearing seat means isprovided with a generally annular sealing wall having an inner and outersurface and extending from said bearing seat means coaxial with saidscrew flight section, said outer surface disposed closely adjacent saidinternal screw flight; and a secondary internal screw flight means issecured to said shaft closely adjacent said inner wall.
 4. The inventionof claim 3 in which said secondary internal screw flight means isfurther defined by a generally annular element coaxial with said screwflight section and having a screw flight on the external surfacethereof. ,
 5. The invention of claim 4 in which said secondary internalscrew flight element is operatively secured to said shaft by means offasteners extending through a radial shoulder of said element into aradial shoulder of said screw flight section.
 6. The invention of claim2 in which said bearing seat means is further provided with a sealextending from said bearing seat means into contact with said shaftwhereby lubricating oil can be retained in said bearing and steam andother vapors are precluded from coming into contact with said bearing.7. The invention of claim 1 in which said bearing seat means dependsfrom said die plate means.
 8. The invention of claim 7 in which said dieplate means is further defined by a generally circular plate secured tosaid housing in blocking relationship to said output end with said shaftend disposed within said housing, the internal wall of said plateincluding a bearing boss defining said bearing seat means.
 9. Theinvention of claim 8 in which a cutter bearing seat is provided in theexternal surface of said plate and is adapted to receive a rotatingcutter driven independently of said shaft.
 10. A dewatering pelletizerfor dewatering and reducing the size of wet polymeric materialcomprising in combination: an elongated barrel housing defined by aplurality of slightly spaced screen bars defining escape passagesthrough which liquid can be forced, said barrel housing having an inputend and an output end; a rotatable shaft disposed axially within saidhousing, said shaft having a first and extending through said housingand supported for rotation by means of a bearing and adapted to bedriven by a suitable power source, and a second end disposed within saidoutput end of said barrel housing; a plurality of dewatering screwflights carried by said shaft and including a generally annular screwflight section adjacent said second end and defining with the internalwall of said barrel housing a generally annular space; a generallyannular die plate secured to said housing at said output end; agenerally circular support member secured to said die plate coaxial withsaid rotatable shaft; a generally annular bearing boss secured to saiddie plate and disposed coaxial with said rotatable shaft, said bearingboss including a bearing seat adapted to receive a bearing providingrotatable support for said second end of said rotatable shaft; vaporsealing means extending from said bearing boss into contact with saidrotatable shaft, said sealing means and said bearing boss defining alubrication chamber for said bearing; circumferentially spaced taperedapertures in said die Plate for the passage of polymeric materialtherethrough; said generally annular screw flight section defined byexternal and internal screw flights; a generally annular sealing wallhaving an inner and outer surface and extending from said bearing bosscoaxial with said shaft, said outer surface disposed closely adjacentsaid internal screw flight of said annular screw flight section; asecondary internal screw flight defined by a generally annular elementcoaxial with said shaft and operatively secured to said shaft and havinga screw flight on the external surface thereof and having a screw flightclosely adjacent said inner surface of said sealing wall; a cutterbearing seat in said support member; a rotatable cutter shaft supportedby said cutter bearing seat and adapted to be driven by an externalpower source independently of said rotatable shaft; a plurality ofspaced cutter knives mounted on said cutter shaft, each cutter knifehaving a sharp leading edge and so positioned with respect to said dieplate that they meet the extruded material while the material issupported by the walls of the die plate defining said tapered aperturesas it is forced from said die plate.